An image processing apparatus is known that inputs drawing commands specified with an RGB color space to generate bitmap data of a color space of C (cyan), M (magenta), Y (yellow) and K (black) in order to reproduce colors corresponding to the drawing commands in a printer or the like. In this type of apparatus, when instructed to perform compensation of gray according to the type of object, for example, characters, graphics or images of the drawing commands, if R (red)=G (green)=B (blue) in the RGB data of a pixel, then the color of the pixel is judged to be an achromatic color and that RGB data is converted to K (black) data (Y=M=C=0).
Further, in an image processing apparatus that enters drawing commands specified with a CMYK color space to generate color bitmap data for a CMYK color space of a device, when in an input pixel value of a CMYK color space, a value of cyan is equal to a value of magenta and yellow (C=M=Y), the color of the input pixel is taken as an achromatic color and a compensation of monochrome K is performed (see Japanese Patent Laid-Open No. 09-277606).
Thus, conventionally the compensation of a single color has been limited to black only, and it was not possible to compensate another single color, for example, each of the coloring materials of C, M and Y. Furthermore, for secondary colors (realized using a plurality of coloring materials, for example, green (G) obtained by a mixture of cyan ©) and yellow (Y)) also, such color compensation could not be effected.